In a conventional internal combustion engine, engine wear is reduced and operational efficiency and fuel consumption are improved if engine vibration is minimized, or some of the pistons can be deactivated at certain times when full power is not required. Vibration is reduced in an engine that is dynamically balanced. But a conventional engine which has only one crankshaft and four, six or eight pistons firing in sequence, is difficult to dynamically balance. Balance can be improved if the engine has more than one crankshaft.
In a conventional internal combustion engine, the speed of the engine is measured in rotations per minute (“rpm”) of the crankshaft. Operating an engine at higher rpm means that the pistons go through more cycles over a given time. Thus the moving engine parts travel larger distances and engine wear is increased. While conventional internal sequential piston fired combustion engines with one crankshaft are inherently not dynamically balanced, they achieve better balance when operated at higher rpm. The higher rpm tends to override imbalance. An engine which has two crankshafts and accompanying pairs of pistons and cylinders provides better balance and operates smoothly at lower rpm. Supercharging engines which operate at higher compression ratios improve fuel combustion efficiency and conserve fuel.
U.S. Pat. No. 5,758,610, granted Jun. 2, 1998 to Gile Jun Yang Park, discloses an air-cooled self-supercharging four stroke internal combustion engine having four pistons which move in unison. There are two downward piston strokes in each four stroke cycle. The downward strokes of the pistons are used to compress the air in the crank case and supercharge the engine by forcing the more air and fuel into the two combustion chambers. Each combustion chamber serves two piston cylinders. The compressed air and fuel mixture is forced into only one combustion chamber during each downward stroke of the pistons. The two combustion chambers are charged with air and fuel on alternating downward piston strokes. The engine is air-cooled by the flow of the combustion intake air which passes through the crank case. At the same time, heat transferred from the engine pre-heats the intake air to improve combustion efficiency. The technology disclosed in U.S. Pat. No. 5,758,610 is incorporated herein by reference.
U.S. Pat. No. 6,318,310 B1, granted Nov. 20, 2001 to Clarke, discloses a dual mode internal combustion engine which may operate in either a power mode or an efficient mode. The dual mode internal combustion engine has two four-cycle combustion chambers and a two-cycle compression/expansion chamber. The valve system is set up to introduce a fluid charge into the compression/expansion cylinder during the power mode. The fluid charge is compressed in the compression/expansion chamber and one of the combustion chambers. During the efficiency mode, the fluid charge is expanded first in one of the combustion chambers and further expanded in the compression/expansion chamber.
U.S. Pat. No. 7,080,622 B1, issued Jul. 25, 2006 to Belloso, discloses a multi-cylinder internal combustion engine for a wheeled vehicle which is divided into at least two power producing sub-units designated primary and secondary sub-units. The primary sub-unit operates during all powered movement of the vehicle. The secondary sub-unit is activated only when additional power is needed. When inactive, no fuel is delivered to the secondary sub-unit, and there is no movement of its components. Each sub-unit has its own crankshaft, and the crankshafts are connected by a clutch mechanism interactive with a single output shaft that delivers power to the wheels of the vehicle.
U.S. Pat. No. 7,032,385 B2, issued Apr. 25, 2006 to Gray, Jr., discloses an internal combustion engine for a vehicle which provides variable displacement by selectively driving one or more engine crankshafts mounted within a single unitary engine block. In several embodiments, the crankshafts are connected to a common output shaft with a one-way clutch between the common output shaft and at least one of the crankshafts. In one aspect, starter gearing is independently associated with each of the first and second crankshafts and a starter is provided for selective engagement with the starter gearing of either of the crankshafts. In another aspect, an accessory drive for driving accessory systems of the vehicle receives power from any crankshaft which is operating, yet is isolated from any crankshaft that is not operating by a one-way clutch.